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Date:   Sat, 26 Jun 2021 23:24:07 +0000
From:   Jonathan =?utf-8?Q?Neusch=C3=A4fer?= <j.ne@posteo.net>
To:     Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        linuxppc-dev@lists.ozlabs.org, devicetree@vger.kernel.org,
        Ash Logan <ash@heyquark.com>,
        Jonathan =?utf-8?Q?Neusch=C3=A4fer?= <j.ne@posteo.net>,
        Rob Herring <robh+dt@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/4] nvmem: nintendo-otp: Add new driver for the Wii
 and Wii U OTP
Message-ID: <YNe3F7DPOOKuaFIm@latitude>
References: <20210519095044.4109-1-linkmauve@linkmauve.fr>
 <20210519095044.4109-2-linkmauve@linkmauve.fr>
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Hi,


On Wed, May 19, 2021 at 11:50:41AM +0200, Emmanuel Gil Peyrot wrote:
> This OTP is read-only and contains various keys used by the console to
> decrypt, encrypt or verify various pieces of storage.
>=20
> Its size depends on the console, it is 128=C2=A0bytes on the Wii and
> 1024=C2=A0bytes on the Wii=C2=A0U (split into eight 128=C2=A0bytes banks).
>=20
> It can be used directly by writing into one register and reading from
> the other one, without any additional synchronisation.
>=20
> Signed-off-by: Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
> ---

A link to the (third-party) documentation would be nice, either in the
commit message or in the code itself.

(https://wiiubrew.org/wiki/Hardware/OTP i guess)

[...]
> +static int nintendo_otp_reg_read(void *context,
> +				 unsigned int reg, void *_val, size_t bytes)
> +{
> +	struct nintendo_otp_priv *priv =3D context;
> +	u32 *val =3D _val;
> +	int words =3D bytes >> 2;
> +	u32 bank, addr;
> +
> +	while (words--) {
> +		bank =3D (reg << 1) & ~0xff;

This is a bit non-obvious, IMHO. As far as I understand it, the expanded
formula is:

	bank =3D (reg / 128) << 8;

I.e. first divide by bank size, then shift the parameter into the right
place.

> +		addr =3D (reg >> 2) & 0x1f;

Here, I think it's about the word size (4 bytes); I think / 4 would be
clearer.

I *think* (but haven't checked) that gcc should generate efficent shifts
for the divisions above, so using the division operator shouldn't be
problem.

> +		iowrite32be(OTP_READ | bank | addr, priv->regs + HW_OTPCMD);
> +		*val++ =3D ioread32be(priv->regs + HW_OTPDATA);
> +		reg +=3D 4;
> +	}
> +
> +	return 0;
> +}
> +
[...]
> +	if (of_id->data) {
> +		const struct nintendo_otp_devtype_data *data =3D of_id->data;
> +		config.name =3D data->name;
> +		config.size =3D data->num_banks * 128;

Given that 128 appears a few times, perhaps a #define would be good.

> +	}
> +
> +	config.dev =3D dev;
> +	config.priv =3D priv;
> +
> +	nvmem =3D devm_nvmem_register(dev, &config);
> +
> +	return PTR_ERR_OR_ZERO(nvmem);
> +}
> +
> +static struct platform_driver nintendo_otp_driver =3D {
> +	.probe =3D nintendo_otp_probe,
> +	.driver =3D {
> +		.name =3D "nintendo-otp",
> +		.of_match_table =3D nintendo_otp_of_table,
> +	},
> +};
> +module_platform_driver(nintendo_otp_driver);
> +MODULE_AUTHOR("Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>");
> +MODULE_DESCRIPTION("Nintendo Wii and Wii U OTP driver");
> +MODULE_LICENSE("GPL v2");
> --=20
> 2.31.1
>=20

Tested-by: Jonathan Neusch=C3=A4fer <j.ne@posteo.net>  # on Wii


Thanks,
Jonathan Neusch=C3=A4fer

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